The present invention generally relates to methods of producing semiconductor devices, and in particular to methods of producing semiconductor devices using copper or copper alloys as a wiring or metallization material.
It is known, that a metallization pattern of a large scale integrated circuit (LSI) diminishes in width as its integration density increases. Although aluminum (Al) metallization is widely used for semiconductor chips, its width for metallization is limited to the range of 0.5 to 0.6 .mu.m. This is because electromigration increases as the aluminum metallization pattern becomes narrower. For these reasons, the use of a metallic material of a high melting point such as molybdenum (Mo) or tungsten (W) in place of Al has been considered. However, the resistivity of Mo and W is approximately twice the resistivity of Al in bulk and is even greater in a thin film. Therefore, need exists for a metallization material having a high electromigration resistance and a low resistivity.
Presently, copper (Cu) is being investigated for metallization of LSIs due to its better electromigration resistance and lower resistivity than Al. A conventional semiconductor device with copper metallization is designed so that a copper metallization film is directly deposited on an insulating film such as silicon dioxide (SiO.sub.2) which is deposited on a silicon (Si) substrate and over contact holes formed in the insulating film so as to be positioned on diffused layers formed in the Si substrate. The copper film then patterned in accordance with a wiring pattern.
The semiconductor device thus configured is generally annealed at a high temperature on the order of 400.degree. C. or greater in order to grow grains of Cu and thereby improve the electromigration resistance. Thereafter, an insulating film is deposited on the Cu metallization film as well as the insulating film. The deposition of the insulating film is conventionally carried out by a chemical vapor deposition (CVD) at a temperature of approximately 420.degree. C. The insulating film on the copper metallization film may be made of, for example, phosphosilicate glass (PSG), silicon nitride (Si.sub.3 N.sub.4) or SiO.sub.2. The insulating film acts as a passivation film or a layer-to-layer insulating film in multilevel interconnections.
However, there are disadvantages with the conventional method of producing semiconductor devices with the Cu metallization method mentioned above. That is, the oxidation temperature of Cu ranges from 200.degree. to 250.degree. C., whereas the heat treating temperature in the CVD is on the order of 400.degree. C. or greater. Therefore, Cu in the metallization film is easily oxidized due to oxygen which exists in an ambient atmosphere when depositing the insulating film by the CVD process. Oxidation of Cu damages the surface of the metallization film which is in contact with the insulation film and therefore degrades the Cu metallization film especially in terms of resistance.